Large liquid-scintillator trackers for neutrino experiments
Résumé
Results are given on tests of large particle trackers for the detection of neutrino interactions in long-baseline experiments. Module prototypes have been assembled using TiO$_2$-doped polycarbonate panels. These were subdivided into cells of $\sim 1$~cm$^2$ cross section and 6~m length, filled with liquid scintillator. A wavelength-shifting fibre inserted in each cell captured a part of the scintillation light emitted when a cell was traversed by an ionizing particle. Two different fibre-readout systems have been tested: an optoelectronic chain comprising an image intensifier and an Electron Bombarded CCD (EBCCD); and a hybrid photodiode~(HPD). New, low-cost liquid scintillators have been investigated for applications in large underground detectors. Testbeam studies have been performed using a commercially available liquid scintillator. The number of detected photoelectrons for minimum-ionizing particles crossing a module at different distances from the fibre readout end was 6 to 12 with the EBCCD chain and a mirror at the non-readout end; 4 to 10 with the HPD and no mirror. The light-attenuation lengths in the fibres were $\sim 9.4$~m with the EBCCD and $\sim 6.4$~m with the HPD. The detector response to electron showers has also been measured. After 10 radiation lengths of lead, the transverse position of the incoming electron was determined with a precision of a few millimeters for electrons of 4 GeV, and with a \hbox{precision of 1.5$-$2.0~cm for electrons of 1~GeV.}
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